Down to the sea

By Bryan Walker 06/05/2010


An interview with climatologist Ellen Mosley-Thompson published yesterday in Yale Environment 360 is a reminder that for those working with ice there’s not much doubt about where we’re heading. She spent six weeks of the summer on her ninth visit to Antarctica drilling ice cores on the Antarctic Peninsula, one of the fastest-warming places on earth. Its winter temperatures have increased by 6 degrees over the past 60 years and year-round temperatures by 2.8 degrees. As a result, sea ice now covers the western Antarctic Peninsula three months less a year than three decades ago, 90 percent of glaciers along the western Antarctic Peninsula are in retreat, and large floating ice shelves are crumbling.

Mosley-Thompson headed a team of six for the drilling, and they were part of a larger group attempting to understand the warming behind the break-up of the Larsen B ice shelf in 2002. Ecologists were looking at an ecosystem on the ocean bottom that until eight or nine years ago had been covered by ice for thousands of years and considering how it is adjusting to the new normal. Glaciologists were looking at how much more rapidly the glaciers are discharging into the ocean with the disappearance of the buttressing ice shelf. A marine group was looking at changes in marine geo-chemistry, collecting new cores in the area that was covered by ice to compare with the cores previously drilled in the ocean bottom along the outer margins of Larsen B when it was in place.

It’s an impressive range of investigation she describes. The ice drilling on the Bruce Plateau was able to get right down to bedrock at 455 metres, and the cores will be closely analyzed back in Ohio for the information they contain about past climate, perhaps to the last glacial period and beyond.

Mosley-Thompson is married to Lonnie Thompson, the highly respected glaciologist. While his wife has been working mostly in Greenland and Antarctica he has done more ice corings of low-latitude glaciers —- in the Andes, Africa, and the Himalayas —- than any other person alive. Yale Environment comments that their work, taken together, paints a sobering portrait of the rapid retreat of most of the world’s glaciers and ice caps in the face of the buildup of planet-warming greenhouse gases.

Here are some of the things Mosley-Thompson has to say in the interview about the overall global picture. In response to the interviewer’s observation that the deep Antarctic ice cores taken at Dome C years show that we have got more CO2 in our atmosphere than at any time in 800,000 years:

’Very clearly. If you look back over the eight glacial/interglacial cycles, you essentially see that CO2 never rises above 300 parts per million and we’re at about 389 now. Methane never rises above about 800 parts per billion, and I think we’re at about 1,700 parts per billion. So we’re clearly outside the range of natural variability. I personally think that graph simply showing the natural fluctuations in those two important greenhouse gases, over almost a million years of Earth history – and then you see the two dots [today] that are so much higher than anything that we see in that near-million history – tells us very clearly that we have a serious problem.’

What does the cumulative ice coring  work show about what we’re experiencing in the last century or so in terms of the warming of the planet?

’ Well, from the tropical work, the cores in the Andes and the Himalaya, the oxygen isotopic ratio in those cores, when you stack those cores together, show very clearly that the last 50 or 60 years have been the warmest in the last 2,000 years.’

The ice cores from the Andes do show a Medieval Warm Period signature and a very distinct Little Ice Age cool signature.  Not surprising, she says, because both those periods are expressed most strongly around the Atlantic Basin and the moisture that builds the glaciers in the Andes of Peru actually comes from the Atlantic.  But the cores from the Tibetan Himalaya show virtually no signature of these periods.

’so when we put these records together, the medieval warming is very modest and the Little Ice Age signature is strongly muted as well. And what really stands out when you put these all together and into the composite, is the last 60 years. The oxygen isotopic enrichment in the tops of the cores [indicating warming] is very striking.’

She notes that particularly in the case of the tropical ice fields the glaciers are retreating very rapidly:

“And, in fact, several of the ice fields, particularly one that we recently published the results [for] in the southwestern Himalaya, it has not gained mass or has no ice that was deposited after 1950. It’s like these glaciers are just literally being decapitated. And it’s very frightening.’

And what about the IPCC error on Himalayan melting?

’…when you look at the breadth of the Intergovernmental Panel on Climate Change reports, and how much information is in there, the fact that this must be the most egregious error, otherwise they would be making more of something else —  I think it’s astounding that the IPCC got as much right as they did because there was just tremendous potential for error.’

And if we don’t begin to rein in CO2 emissions, where is the cryosphere, the Earth’s ice zone, heading?

’To the oceans. Ultimately that’s where all water goes, to the lowest level.’